I love Scotland and have been up many times. Our main bases are Aviemore and Fort William, a nice 8 or 9 hour drive from home in Shropshire. The drive up is great once past Manchester and Preston as you then have the Lake District one side and the Yorkshire Dales the other. About 3 years ago we flew up from Birmingham to Inverness, great views flying over the Highlands.
Most of my favourite places have already been mentioned - I'd say Oban, Mallaig, Elgin, Pitlochry, Inveraray and Dunkeld off the top of my head. The beautiful countryside of Perthshire gives way to the Cairngorm National Park. Over Fort William way there's a beautiful drive down through Glencoe to the south or to the north, the road to the isles heading for Mallaig and past the impressive Glenfinnan monument with views of the Harry Potter train passing through the mountains.
I havw also stayed many times in all of the cities. I like the grittiness of Glasgow best then the small city of Inverness, capital of the Highlands. Edinburgh is beautiful but very touristy then there's Aberdeen, Dundee, Stirling and Perth. Like them all for different reasons.
I love the country and looking forward to going again as not been since January 2018.